Study On Pulse Current-Assisted Laser Shock Composite Strengthening Method And Strengthening Effect

Using 2024-T4 aluminum alloy as the research material,using the electroplastic effect of current and laser shock to compound,a new type of metal material strengthening method is proposed.Aiming at the problems of current equipment,insufficient power of laser equipment and local processing of workpieces in practical engineering applications,the paper designs a energization device that can concentrate high-density current in a local area,and can cooperate well with laser shock to complete composite strengthening.The thesis conducts the test,observation and analysis of microhardness,residual stress,fracture morphology and microstructure of aluminum alloy samples under different treatment methods,and studies the composite strengthening effect.The main work and conclusions are as follows:(1)The experiment used a composite strengthening experiment with different energization methods,namely,laser shock under ordinary energization(ELSP1),laser shock under current collecting mode(ELSP2),and laser shock under current direction parallel to the laser direction(ELSP3).The test results indicate that the composite strengthening under the three different energization methods has a better effect than single laser shock strengthening,and the effect of ELSP2 is better than ELSP1.The device can better converge current density to improve the strengthening effect;at the same time,the effect of ELSP3 better than ELSP1,the composite strengthening effect is sensitive to the current direction,and the strengthening effect is better when the current direction is parallel to the laser direction.(2)The surface hardness after laser shock is 143HV,which is 36.2%higher than that of the untreated surface(105HV).The surface hardness after composite strengthening increases with the increase of current density.The surface hardness at 20A/~2is 50.5%higher than that of the untreated surface,which is 158HV.The surface hardness at 40A/~2is 71.4%higher than that of the untreated surface,which is 180HV;composite strengthening can also increase the microhardness value in the depth direction,and the hardness value of 120HV can be maintained at a depth of 1.5mm at 40A/~2;under the same current density(20A/~2),when the current direction is parallel to the laser direction,the composite strengthening slightly increases the surface microhardness and microhardness at different depths.Compared with the non-parallel state(158HV),the surface microhardness increases by 3.9%.The microhardness in depth increased by an average of 7.6%.(3)The average value of the surface residual compressive stress after laser shock is-161.1MPa,and the surface residual compressive stress is further increased after composite strengthening,and increases with the increase of current density.The residual compressive stress increases by 10.7%to-178.4MPa when the current density is 20A/~2;It increases by 40.5%to-226.3MPa when the current density is 40A/~2;In depth,the depth of the compressive stress layer produced by laser shock is 0.75mm?1mm,while in composite strengthening,the depth is 1mm?1.25mm at 20A/~2,and the depth is about 1.5mm at 40A/~2;Under the same current density(20A/~2),when the current direction is parallel to the laser direction,the composite strengthening improves the residual compressive stress and the depth of compressive stress.Compared with the non-parallel state(-178.4MPa),the surface residual compressive stress is increased by 4.9%.The depth has increased by about 0.2mm.(4)After laser shock,the grain size is refined to about 50?m.After composite strengthening,the grain size is further refined.The grain size is about 35?m when the current density is20A/~2and the grain size is about 20?m when the current density is 40A/~2.At the same time,the full width at half maximum of the(200)diffraction crystal plane in the XRD pattern has increased,which also indicates that the degree of refinement is higher after composite strengthening.(5)By observing the fracture morphology of aluminum alloy samples under different treatment methods,it is found that the fracture form of the original aluminum alloy is mainly ductile fracture.After laser shock strengthening,there is a tendency of brittle fracture,the plasticity of aluminum alloy decreases.While the plasticity is slightly improved after composite strengthening because of the effect of pulse current.The higher the current density in a certain range,the more obvious the improvement.At the same time,the tendency of the second-phase particle change also shows that the composite strengthening has the effect of suppressing cracks and promoting dislocations.